The coatings industry is undergoing massive changes in its philosophy, a great deal thereof being the result of the ecological problems associated with the use of the conventional solvent-based coating compositions. In the past the most commonly used coatings were compositions of pigmented or unpigmented liquid vehicles that were diluted with solvents to facilitate application. After application on the surface, the solvents were permitted to evaporate, often into the atmosphere, leaving a dry, uniform coating on the surface. With time, advances led to the development of organosols, plastisols, emulsions, dispersions, 100 per cent reactive solids coatings, water-borne coatings, all of which are used today to some extent. In addition, within the past two decades much effort has been expended in the preparation and application of powder coatings, the initial impetus therefore being the discovery of the fluidized-bed technology in Germany. This initial effort in the powder coating field involves the submersion of a preheated article into a bed of powder particles, the particles generally being from 50 to 150 microns in size, fluidized by a stream of gas. On immersion in the fluidized-bed, powder particles adhere and coalesce on to the surface of the article forming a uniform coating, usually in excess of 5 mils thick and often as much as 100 mils thick. The relatively large particle sizes required for fluidized-bed coating technology precludes the formation of the thin coatings of from 0.2 to 2 or 3 mils thick that are often desired. Many further attempts have been made to apply such thin coatings, the most recent efforts being directed to the electrostatic spray coating of particles to the grounded article to be coated followed by heating to fuse the particles and form a uniform coating. This method has recently been finding wide acceptance because of the many advantages associated therewith, e.g., improved film properties, absence of volatile solvents, elimination of water pollution problems, essentially 100 per cent utilization of material, reduced capital expenditures, ease of change-over.
Among the many powder coatings that have found widespread use are included the epoxy polymers. However, these epoxy materials are known to be deficient in outdoor weathering and in acidic environments. Consequently, it is of interest to obtain new epoxy-type powder coating compositions that do not have these deficiencies.